1. Technical Field of the Invention
The present invention is concerned with devices which provide a detectable indication that a volume of gas has an increased proportion of carbon dioxide compared to that present in normal ambient air. Such devices have a number of uses, one major use being to provide an indication of whether a tube has been correctly located in the airway (trachea) of a patient. There are many clinical situations where it is necessary to place a tube in the trachea of a patient. This is done in order to supply air or a mixture of oxygen and other gases to the lungs of the patient. The correct placement of the tube in the trachea is very important. Accidents have been reported where the tube has been inadvertently placed in the oesophagus. It has been observed that the air in the trachea contains about 6%carbon dioxide, whereas the oesophagus contains air in which the concentration of carbon dioxide is normal (about 0.03%).
2. Description of the Prior Art
Indicator devices which can detect the presence of an elevated proportion of carbon dioxide compared to that in air, and which can be used to determine whether a patient has been correctly intubated are described in U.S. Pat. No. 4728499, W089/07957 and W090/01695.
In all of these indicator devices, an indicator material is dispersed throughout a body of porous material: because the gas to be tested has to be passed through the body, the rate of flow is slow and therefore the response time is unacceptably long.
We have now devised an indicator device which has a rapid response, because of the manner in which the indicator material is provided.